This invention relates generally to a method and apparatus for processing digital images and, in particular, to a method and apparatus for removing random pixels resulting from noise generated by the thresholding operation from a multiple color scale to a two-level (black/white) representation during the development of a facsimile image.
When generating thresholded black and white facsimile images, electronic noise is often generated. Such noise is exhibited as holes or white spots in the middle of dark areas of a figure, single or small groups of black dots in white areas of an image, or unsmooth edges of figures. Noise increases the number of bits which must be transmitted to form a facsimile image. The noise itself does not contain any useful information; thus, by suppressing this noise, visual and machine pattern recognition are greatly aided. Furthermore, noise reduction improves data compression performance, since it improves the line-to-line correlation in its facsimile image, which is the basis of many compression methods. This improves correlation and also results in faster data transmission.